The interaction of radiolabelled human growth hormone (125I-hGH) with isolated target cells, both normal and pathological will be studied. A highly specific growth hormone receptor on isolated hepatocytes has been characterized by both kinetic and equilibrum binding techniques. These studies demonstrated that the hormone receptor interactions are complex, involving allosteric regulation of macro-molecular receptor complexes. The effects of hGH upon amino acid transport and protein synthesis in the hepatocyte have been defined. These cells have been shown to be normally responsive in terms of these biologic endpoints. For these reasons the hepatocyte will prove to be an excellent model in which to study hormone receptor interactions in normal and pathologic states. These studies will be expanded to include isolated hepatoma cells. The necessary methodology to isolate and maintain these cells will first be developed. A direct comparison of hormonal binding, amino acid transport and protein synthesis in the normal hepatocyte and hepatoma cell will then be possible.